Conventionally, inorganic iodide has been synthesized by a variety of methods. For example, Patent Literatures 1 through 7 listed below disclose examples of methods of synthesizing inorganic iodides. Patent Literature 1 discloses a method including adding iodine to an alkaline solution so as to carry out a reaction to give iodate, and then reducing the iodate with aluminum or zinc. Patent Literature 2 discloses a method including adding iodine to an alkaline solution to obtain a solution, and then carry out reduction with hydrogen sulfide. Patent Literature 3 discloses a method including reducing iodine or iodate with alkali metal amalgam in an alkaline environment or in a neutral environment. Patent Literature 4 discloses a method including treating an iodine alkali hydroxide solution with an organic reducing agent such as formic acid, oxalic acid, or malonic acid. Patent Literature 5 discloses a method including adding iodine to a potassium hydroxide solution to obtain a solution, and then reducing the solution with formic acid serving as a reducing agent. Patent Literature 6 discloses a method including reacting iodine with potassium hydroxide or with alkaline carbonate with use of hydrazine serving as a reducing agent. Patent Literature 7 discloses a method of (i) neutralizing a potassium hydroxide solution with use of formic acid so as to obtain a resultant solution, (ii) adding an over-stoichiometric amount of iodine to the resultant solution so that the resultant solution undergoes a reaction, and (iii) treating free iodine in the post-reaction resultant solution with potassium sulfide.